Anion-Directed Metallocages: A Study on the Tendency of Anion Templation.

Research paper by Jing-Yun JY Wu, Ming-Shiou MS Zhong, Ming-Hsi MH Chiang

Indexed on: 13 Sep '17Published on: 13 Sep '17Published in: Chemistry - A European Journal


Self-assembly of Cu(NO3)2∙3H2O and a di(3-pyridylmethyl)amine (dpma) ligand with addition of different acids (HNO3, HOAc, HCl, HClO4, HOTf, HPF6, HBF4, and H2SO4) afforded a family of anion-templated tetragonal metallocages having a cationic prismatic structure of [(Gn-){Cu2(Hdpma)4}](8-n)+ (Gn- = NO3-, PF6-, SiF62-) with different ligating anions/solvents (NO3-, Cl-, ClO4-, OTf-, H2O) outside the cage. The systematic competitive experiments have significantly rationalized a tendency of anion templation towards the formation of metallocages [(Gn-){Cu2(Hdpma)4}](8-n)+ as SiF62- ~ PF6- > NO3- > SO42- ~ ClO4- ~ BF4-. This sequence is mostly elucidated by shape control over size selectivity and electrostatic attraction between the cationic {Cu2(Hdpma)4}8+ host and the anionic guests. In addition, these results have also roughly ranked the anion coordination ability in the order Cl-, ClO4-, OTf- > NO3- > BF4-, CH3SO4-. Magnetic studies of metallacages 1t and 2-4 suggest that the fitted magnetic interaction, being weakly magnetically coupled overall, is interpreted as a result of the combination of intra-cage ferromagnetic coupling integrals and inter-cage antiferromagnetic exchange; both contributions are very weak and comparable in strength.